This invention pertains to strapping machines. More particularly, the present invention pertains to an improved drive arrangement for a strapping machine including a rewind member and cutting arrangement.
Strapping machines are in widespread use for applying a strap, such as a plastic strap, in a tensioned loop around a load. A typical strapping machine includes a strap chute for guiding the strap around the load, a strapping head through which the leading end of the strap is fed, and a strap dispenser to dispense a desired length of strap from a coil of strap material.
The strapping head carries out a number of functions. It advances the strap along the chute around the load until the leading end returns to the strapping head and retracts or rewinds the strap from the chute to produce tension in the strap around the load. The strapping head typically includes an assembly for securing the strap in the tensioned loop around the load such as by welding the strap to itself at its overlapping portions.
A typical strapping head includes a pair of advancing rollers for advancing the strap through the strapping head and a pair of retraction rollers for retracting the strap to, for example, take-up the strap. The head also includes a winder or tensioner that rewinds or takes up the strap after it is positioned around the load so as to apply a tension in the strap. In one known configuration, the winder includes a split-type rotating element that has a channel or slot formed therethrough to essentially define split halves of the winder. The split halves are fixed relative to one another and the strap traverses through the slot between the halves. Upon an appropriate signal, the winder is actuated and rotates to tension the strap.
In a typical winder arrangement, the strap is not in tension until it passes over itself around the winder, thus creating sufficient friction to prevent the strap from slipping through the winder slot. It has been observed that often, the winder must rotate in excess of 360 degrees, and with some types of readily compressible loads, it must rotate more than 720 degrees to provide sufficient friction to begin tensioning and to provide the appropriate tension on the strap.
In known strapping heads, the winder is positioned intermediate the feed and retraction rollers. An arrangement such as this disclosed in U.S. Pat. No. 4,605,456 which patent is assigned to the assignee of the present application and is hereby incorporated by reference. Although the strapping machine disclosed in this patent functions well, it does have certain drawbacks. For example, it has been found that in known strapping machines, the strap may not automatically refeed after faulted strap is ejected following a jam in the machine or after significant rewinding following load compression. It has also been found that in known strapping head configurations, adjustments may also be necessary in order to accommodate varying gauges of the strap material. It has further been found that the rewinding length may be limited due to structural constraints of the strapping head, winder and drive arrangement.
Accordingly, there exists a need for a strapping machine having a winder that commences effective tensioning of the strap without the strap having to wind over itself. Desirably, such a winder is effective over a range of strap gauges and can be used with highly compressible loads. More desirably, such a winder permits positioning the winder within the strapping head so as to take advantage of automatically refeeding the strap through the strapping heading following faulted strap ejection.
A strapping machine for positioning a strap material around an associated load and tensioning the strap material around the load includes a frame for supporting the load, a chute positioned on the frame for receiving the strap material and orienting the strap material around the load, a strap supply and a strapping head for extracting the strap from the supply, feeding the strap through the chute around the load, passing the strap from the chute around the load, retracting and tensioning the strap.
The strapping head includes feed rollers and retraction rollers for feeding and retracting the strap and a winder for tensioning the strap around the load. Preferably, the winder includes a rotating head portion having a stationary element and a pivotal element, each defining an outer surface around which the strap material is wound. The stationary and pivotal elements define a slot therebetween for receiving the strap material. Each element defines a gripping portion at about a respective end that is opposingly facing the other of the gripping portions.
The pivotal element is pivotal between an open position in which the gripping portions are spaced from one another and a closed position in which the gripping portions cooperate with one another to engage and secure the strap material therebetween. The winder rotates from a home position in which the winder is in the open position and an other than home position in which the winder is in the closed position to exert a tension in the strap. In a most preferred embodiment, the winder is positioned between the feed and retraction rollers and the strap supply.
In a preferred winder, the pivotal element is biasedly mounted to the head portion into the closed position and includes a projection extending from the pivotal element for maintaining the pivotal element in the open position when the winder is in the home position.
The winder includes a drive assembly for rotating the winder head portion. Preferably, the winder includes a winder biasing element, such as a clock-type spring for returning the winder to the home position.
The strapping machine can include one or more intermediate stop plates positioned between the winder head portion and the frame. The intermediate stop plates permit greater than 360 degree rotation of the winder relative to the strapping machine.
A preferred embodiment of the strapping machine includes a cam having a feed surface, a retraction surface and an intermediate surface and a linkage assembly for actuating the feed rollers, the retraction rollers and the winder. The preferred linkage includes a single cam-contacting linkage arm configured to bear against the cam.
The linkage is configured to move the feed rollers into engagement with the strap material and to move the retraction rollers out of engagement with the strap material when the cam-contacting linkage arm bears against the feed surface. The linkage is further configured to move the retraction rollers into engagement with the strap material and to move the feed rollers out of engagement with the strap material when the cam-contacting linkage arm bears against the retraction surface. The linkage further moves the feed rollers and the retraction rollers out of engagement with the strap material when the cam-contacting linkage arm bears against the intermediate surface.
To this end, the linkage assembly includes a second linkage arm configured to bear against the single, cam-contacting linkage arm. The cam-contacting linkage arm is configured to move the feed rollers into and out of engagement with the strap material and the second linkage arm is configured to move the retraction rollers into and out of engagement with the strap material.
A most preferred embodiment of the strapping machine includes a cutting assembly positioned between the feed rollers and the retraction rollers. The cutting assembly includes a stationary anvil and a rotating cutting blade defining a pivot. The cutting assembly further includes a drive assembly having a motor and a cam-follower mounted thereto.
A linkage member is operably mounted to the rotating cutter and has an elongated slot formed therein. The cam-follower is configured for receipt in and movement through the elongated slot. Actuation of the motor moves the cam-follower through the elongated slot to rotate the blade into engagement with the anvil. The blade engages the anvil when the cam-follower is at about a farthest-most position from the pivot.
In a preferred embodiment, the retraction rollers engage the strap following actuation of the cutting assembly. Most preferably, an ejection chute disposed between the feed rollers and the retraction rollers, and the faulted strap is ejected by the retraction rollers through the chute.
Other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims.